update book code

eBook/exercises/chapter_13/panic_defer_convint.go

@@ -0,0 +1,44 @@
+// panic_defer_convint.go
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+func main() {
+	l := int64(15000)
+	if i, err := IntFromInt64(l); err!= nil {
+		fmt.Printf("The conversion of %d to an int32 resulted in an error: %s", l, err.Error())
+	} else {
+		fmt.Printf("%d converted to an int32 is %d", l, i)
+	}
+	fmt.Println()
+	l = int64(math.MaxInt32 + 15000)
+	if i, err := IntFromInt64(l); err!= nil {
+		fmt.Printf("The conversion of %d to an int32 resulted in an error: %s", l, err.Error())
+	} else {
+		fmt.Printf("%d converted to an int32 is %d", l, i)
+	}
+}
+
+func ConvertInt64ToInt(l int64) int {
+    if math.MinInt32 <= l && l <= math.MaxInt32 {
+        return int(l)
+    }
+    panic(fmt.Sprintf("%d is out of the int32 range", l))
+}
+
+func IntFromInt64(l int64) (i int, err error) {
+    defer func() {
+        if e := recover(); e != nil {
+            err = fmt.Errorf("%v", e)
+        }
+    }()
+    i = ConvertInt64ToInt(l)
+    return i, nil
+}
+/* Output:
+15000 converted to an int32 is 15000
+The conversion of 2147498647 to an int32 resulted in an error: 2147498647 is out of the int32 range
+*/